High strength low friction engineered material for bearings and other applications

ABSTRACT

A high strength, low friction engineered material includes a low friction material filling interstices of a metal microlattice. The metal typically comprises 5 volume % to 25 volume % and the interstices typically comprise 75 volume % to 95 volume %, based on the total volume of the metal microlattice and the interstices. The low friction material preferably fills 100 volume % of the interstices. The metal microlattice can be formed of a single layer, or multiple layers, for example layers of nickel, copper, and tin. The low friction material is typically a polymer, such as polytetrafluoroethylene (PTFE), polyamide (PAI), polyetheretherketone (PEEK), polyethylene (PE), or polyoxymethylene (POM). The low friction material can also include additive particles to modify the material properties. The engineered material can be used in various automotive applications, for example as a bearing, or non-automotive applications.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patentapplication Ser. No. 61/728,315, filed Nov. 20, 2012, and U.S.provisional patent application Ser. No. 61/815,480, filed Apr. 24, 2013,the entire contents of which are hereby incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relatives generally to engineered materials, and moreparticularly to high strength, low friction materials, and methods offorming the same.

2. Related Art

Polymer materials are useful in many applications where two surfacesmeet and need to match, such as bearings, gaskets, seals, wipers, andsimilar applications. Polymer materials provide good conformability,despite any wear, defects, or unplanned conditions, and also provide lowfriction, which permits the two surfaces to slide against one anotherwith low forces and very little heat. Another advantage provided bypolymer materials is corrosion resistance. However, the strength ofpolymer materials is relatively low compared to metals, so the use ofplastic materials is limited in applications where applied loads becomeexcessive, such as in automotive bearings.

SUMMARY OF THE INVENTION

One aspect of the invention provides an engineered material comprising amicrolattice formed of metal, and a low friction material disposed inthe interstices of the metal microlattice. The low friction material hasa coefficient of friction less than a coefficient of friction of themetal microlattice.

Another aspect of the invention provides a method of forming theengineered material. The method includes forming the microlattice ofmetal, and disposing the low friction material in the interstices of themetal microlattice.

The engineered material provides advantages of both metal and plasticsimultaneously. The metal microlattice provides strength sufficient towithstand applied loads while requiring a relative low amount of metal,compared to conventional products used for the same application. Thus,the engineered material is more economical to manufacture compared tothe conventional products. At the same time, the low friction materialprovides conformability and low friction. When the low friction materialcomprises a polymer, it also provides corrosion resistance and permitssliding against another surface with low force and low heat.

Another aspect of the invention provides a bearing formed of theengineered material, and a method of forming the bearing comprising theengineered material. The engineered material can be attached or bondedto another solid structure, for example a bronze or steel backing of thebearing. However, the engineered material is also strong enough to standon its own. Thus, a bearing formed of the engineered material is capableof supporting applied loads with less metal and thus lower costs,compared to conventional bearings. In addition, the high amount of lowfriction material performs well in high speed and stop-startapplications, eliminates the need for a 100% polymer coating, and alsoallows the bearing to be machined without loss of performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a magnified view of an engineered material including a metalmicrolattice and low friction material according to an exemplaryembodiment of the invention;

FIG. 1A is an enlarged cross-sectional view of a portion of theengineered material of FIG. 1;

FIG. 2 is a bearing including the engineered material according to anexemplary embodiment of the invention;

FIG. 3 illustrates a method of forming the engineered material accordingto an exemplary embodiment;

FIG. 4 illustrates the step of forming a template polymer microlattice;

FIG. 5 shows three exemplary template polymer microlattices formed bythe step of FIG. 4;

FIG. 6 is a magnified view of a template polymer microlattice formed bythe step of FIG. 4; and

FIG. 7 illustrates the metal microlattice prior to applying the lowfriction material according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENT

Referring to the Figures, wherein like numerals indicate correspondingparts throughout the several views, an engineered material 20 providinghigh strength and low friction is generally shown in FIG. 1. Theengineered material 20 can be used in a variety of applicationsrequiring high strength and/or low friction, including automotive andnon-automotive applications. The engineered material 20 includes a metalmicrolattice 22 providing strength to withstand applied loads, and a lowfriction material 24 disposed in interstices 26 of the metalmicrolattice 22 to provide conformability, low friction, and corrosionresistance.

The metal microlattice 22 is formed of metal; which can be any type ofmetal or metal alloy providing strength sufficient to withstand theloads encountered in the application for which the engineered material20 is designed. In one exemplary embodiment, the engineered material 20is designed to provide a sliding surface 28 of an automotive bearing 30,as shown in FIG. 2, and the metal microlattice 22 is formed of nickel ora nickel alloy. The metal microlattice 22 can be designed with highpercentages of metal at the more highly loaded locations compared to thelightly loaded locations. The metal microlattice 22 can include onelayer 32 of metal, or a plurality of layers 32 of metal, for examplelayers 32 of nickel, copper, and tin. The layers 32 can have the samecomposition as one another or different compositions. In one embodiment,when the layers 32 have different metal compositions, the metal layers32 are alloyed together, for example by a heat treatment process.

As shown in FIG. 1, the metal microlattice 22 of the engineered material20 comprises a plurality of struts 34 interconnected to one another andpresenting a plurality of interstices 26. The metal microlattice 22 istypically present in an amount of approximately 5 to 25 volume % and theinterstices 26 are present in an amount of approximately 75 to 95 volume%, based on the total volume of the metal microlattice 22 and theinterstices 26. In the exemplary embodiment, the metal microlattice 22is present in an amount of 85 volume % and the interstices 26 arepresent in an amount of 15 volume %, based on the total volume of themetal microlattice 22 and the interstices 26. Prior to applying the lowfriction material 24, the interstices 26 are filled with air and thusthe metal microlattice 22 is very light in weight and behaves similar toan elastomer. For example, when compressed, the metal microlattice 22almost completely recovers to its original shape.

Each strut 34 of the metal microlattice 22 is typically disposed at anangle α of 50° to 90° relative to horizontal and has a diameter D in themicrometer range. In the exemplary embodiment, the diameter D of eachstrut 34 is about 50 micrometers. As shown in FIG. 1A, each of thestruts 34 comprises a wall surrounding a center axis and presents anopening 38, which may be hollow or alternatively filled with a templatepolymer. The wall thickness t surrounding the hollow opening 38 can beany thickness t in the micrometer range, for example 5 to 20micrometers. In the exemplary embodiment, the wall thickness t is about15 micrometers. The metal microlattice 22 can comprise a two dimensionalor three dimensional structure. In one embodiment, the metalmicrolattice 22 comprises a three dimensional structure and presents atotal thickness of about 100 μm to 5 cm.

The low friction material 24 preferably fills 100 volume % of theinterstices 26. The low friction material 24 has a coefficient offriction less than the coefficient of friction of the metal microlattice22 and can comprise a variety of different materials. In the exemplaryembodiment, the low friction material 24 is a polymer-based materialincluding at least one of polytetrafluoroethylene (PTFE), polyamideimide(PAI), polyetheretherketone (PEEK), polyethylene (PE), andpolyoxymethylene (POM). The low friction material 24 can alternativelybe formed of tin, lead, bismuth, or alloys thereof. In one embodiment,the low friction material 24 includes particles selected from the groupconsisting of ceramic, such as oxides, nitrides, phosphides, andcarbides; graphite; boron nitride; molybdenum disulfide; copper; andsilver. For example, hard particles can be added for wear resistance,lubricating particles can be added to further reduce friction. Theparticles can also include antimicrobial additives, such as Cu and/orAg. Examples of commercially available low friction materials 24 includeGLYCODUR®, G-92, and IROX®.

The engineered material 20 includes the metal microlattice 22 in anamount of 0.5 volume % to 90 volume % and the low friction material 24in an amount of 10 volume % to 99.5 volume %, based on the combinedtotal volume of the metal microlattice 22 and the low friction material24. However, the amount of low friction material 24 relative to themetal microlattice 22 can vary depending on the application andperformance desired. In the exemplary embodiment, the engineeredmaterial 20 includes the metal microlattice 22 in an amount of 10 volume% to 50 volume %, and the low friction material 24 in an amount of 50volume % to 90 volume %, based on the total volume of the metalmicrolattice 22 and low friction material 24.

The engineered material 20 provides the advantages of both metal andplastic simultaneously. The metal microlattice 22 provides strengthsufficient to withstand applied loads while requiring a relatively lowamount of metal, compared to conventional products used for the sameapplication. Thus, the engineered material 20 is more economical tomanufacture compared to comparative conventional products. At the sametime, the low friction material 24 provides conformability and lowfriction. When the low friction material 24 comprises a polymer, it alsoprovides corrosion resistance and permits sliding against anothersurface with low force and low heat.

A wide variety of desired properties can be achieved by adjusting thecomposition of the metal and low friction material 24, as well as thedesign of the metal microlattice 22. Furthermore, the engineeredmaterial 20 can be attached or bonded to another solid structure, forexample a bronze or steel backing 40 of the bearing 30. However, theengineered material 20 is typically strong enough to stand on its own.The engineered material 20 is especially good for bearing applications,as the metal microlattice 22 supports the applied loads with less metaland thus lower costs, compared to conventional bearings. In addition,the high amount of low friction material 24 performs well in high speedand stop-start applications, eliminates the need for a 100% polymercoating, and also allows the bearing 30 to be machined without loss ofperformance.

Another aspect of the invention provides a method of forming theengineered material 20 by forming the microlattice of metal, anddisposing the low friction material 24 in the interstices 26 of themetal microlattice 22. FIG. 3 illustrates the method steps according toone exemplary embodiment.

The method of forming the engineered material 20 first includespreparing a template polymer microlattice 42 having a predeterminedstructure that will provide the structure of the finished metalmicrolattice 22. The template polymer microlattice 42 is preferablyformed from a ultra-violet (UV) curable resin, also referred to as anegative resist photomonomer. In the exemplary embodiment, as shown inFIG. 4, a reservoir 44 of the UV curable resin in liquid form isprovided, and a perforated mask 46 is disposed over the reservoir 44.The method next includes passing multiple beams of UV light 36 throughthe perforated mask 46 and into the reservoir 44. The UV light 36travels along predetermined paths, which depend on the desired structureof the template polymer microlattice 42 to be formed. The UV light 36then transforms the liquid UV curable resin from UV-opaque toUV-transparent, and also from a liquid monomer to a solid polymer alongthe predetermined paths. The UV light beams 36 are able to penetratedeeper into the reservoir 44 along the solid polymer. The remainingliquid monomer beneath and in-line with the light beam 36 thentransforms to solid polymer, thus self-propagating waveguide formation.By aligning the UV light beams 36 at different intersecting angles, aplurality of interconnected solid polymer fibers 48 are formed, whichtogether form the template polymer microlattice 42. The step ofpreparing the template polymer microlattice 42 is a continuous processwhich can occur at a rate greater than 1 mm² per minute.

FIG. 5 illustrates example designs of the template polymer microlattice42 formed by the exemplary method, and FIG. 6 is a magnified view of athree dimensional template polymer microlattice 42 according to oneexemplary embodiment. Typically, the solid polymer fibers 48 of thetemplate polymer microlattice 42 each extend at an angle α of 50° to 90°relative to horizontal. The solid polymer fibers 48 are also spaced fromone another and thus provide a plurality of interstices 26 therebetween.The template polymer microlattice 42 can comprise two or threedimensions, depending on the desired application or performancerequired. The template polymer microlattice 42 can also be formed orbent into various different shapes, depending on the application andperformance desired.

The method next includes coating the template polymer microlattice 42with the metal to form the metal microlattice 22. As discussed above,any type of metal or metal alloy can be used to form the metalmicrolattice 22. In the exemplary embodiment, the engineered material 20is designed to provide the sliding surface 28 of the automotive bearing30, as shown in FIG. 2, and thus is formed of nickel or a nickel alloy.The step of coating the template polymer microlattice 42 can includeplating or electrodepositing the metal onto the template polymermicrolattice 42, or alternatively can comprise an electroless process.The coating step includes forming a plurality of the metal struts 34surrounding the solid polymer fibers 48. The metal struts 34 areinterconnected to one another and present the plurality of interstices26 therebetween. Thus, the interconnected struts 34 form the metalmicrolattice 22 having a design matching the design of the templatepolymer microlattice 42. In one embodiment, the method includes forminga design with additional struts 34 or more closely spaced struts 34 inone area of the template polymer microlattice 42 relative to the otherareas of the template polymer microlattice 42, and thus applying agreater amount of the metal to one area of the template polymermicrolattice 42 relative to other areas of the template polymermicrolattice 42. According to another embodiment, the method includesapplying multiple layers 32 of the metal to the template polymermicrolattice 42. For example, the method of FIG. 3 includes electrolessplating a layer 32 of nickel, followed by electroplating a layer 32 ofcopper and then a layer 32 of tin, as shown in FIG. 1A.

The method optionally includes removing the template polymermicrolattice 42 from the metal microlattice 22 by heating the templatepolymer microlattice 42. Various different methods can be used to removethe template polymer microlattice 42. For example, after coating themetal microlattice 22, the two microlattices 22, 42 can be heat treatedto melt the template polymer microlattice 42. The template polymermicrolattice 42 is then removed so that only the metal microlattice 22remains. When the metal microlattice 22 includes multiple layers 32 ofdifferent metals, the heating step used to remove the template polymermicrolattice 42 can simultaneously alloy the different metal layers 32together. Alternatively, the step of alloying the different metal layers32 together can be conducted after removing the template polymermicrolattice 42. FIG. 7 illustrates the metal microlattice 22 after thetemplate polymer microlattice 42 has been removed, according to oneexemplary embodiment. In another embodiment, at least a portion of thetemplate polymer microlattice 42 remains in the openings of the metalstruts 34 and thus in the finished engineered material 20.

Prior to applying the low friction material 24 to the metal microlattice22, the method can include attaching the metal microlattice 22 toanother structure. For example, the method can include attaching theengineered material 20 to the backing 40 to form the bearing 30 of FIG.2. Alternatively, the metal microlattice 22 can be used on its own.

The method next includes applying the low friction material 24 to themetal microlattice 22 and disposing the low friction material 24 in theinterstices 26 of the metal microlattice 22 to form the engineeredmaterial 20. The metal microlattice 22 acts as a skeleton, providingsupport and strength, while the low friction material 24 provides aconforming, low friction surface. The step of applying the low frictionmaterial 24 can include rolling the low friction material 24 onto themetal microlattice 22, or infiltrating the low friction material 24 intothe interstices 26 of the metal microlattice 22. The low frictionmaterial 24 is preferably applied so that it fills 100 volume % of thetotal volume of the interstices 26.

After applying the template polymer microlattice 42, the method caninclude machining the engineered material 20 to the desired dimensions.The method can also include applying the engineered material 20 toanother component, such as the backing 40 of the bearing 30. If the lowfriction material 24 includes a polymer, then method can includesintering the engineered material 20 to promote cross-linking of thepolymer. Typically, due to the high amount of low friction material 24,no additional polymer coating is required, such as when the engineeredmaterial 20 is used as the sliding surface 28 of the bearing 30.

The finished engineered material 20 can be used in various automotiveapplications in addition to bearings, such as gaskets, seals, andwipers. Alternatively, the engineered material 20 can be used innon-automotive applications requiring high strength and low friction.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings and may be practicedotherwise than as specifically described while within the scope of theappended claims.

What is claimed is:
 1. An engineered material, comprising: amicrolattice formed of metal, said metal microlattice presenting aplurality of interstices; a low friction material disposed in saidinterstices of said metal microlattice; said low friction materialhaving a coefficient of friction less than a coefficient of friction ofsaid metal microlattice; and wherein said metal microlattice is presentin an amount of approximately 15 volume % and said interstices arepresent in an amount of approximately 85 volume %, based on the totalvolume of said metal microlattice and said interstices; said metalmicrolattice is formed of nickel; said metal microlattice comprises aplurality of struts interconnected to one another and presenting saidinterstices; each of said struts includes a hollow opening; each of saidstruts is disposed at an angle of 50° to 90° relative to horizontal, hasa diameter of about 50 micrometers, and a wall thickness of about 15micrometers surrounding said hollow opening; said low friction materialfilling said interstices; said low friction material including at leastone of polytetrafluoroethylene (PTFE), polyamide (PAI),polyetheretherketone (PEEK), polyethylene (PE), polyoxymethylene (POM),tin, and bismuth; and said low friction material including particlesselected from the group consisting of ceramic, graphite molybdenumdisulfide, copper, and silver.
 2. The engineered material of claim 1,wherein said low friction material includes polyamide (PAI).
 3. Theengineered material of claim 2, wherein said added particles include atleast one of graphite and molybdenum disulfide.
 4. The engineeredmaterial of claim 1, wherein said low friction material includes across-linked polymer.
 5. The engineered material of claim 1, whereinsaid metal microlattice includes a plurality of different metal layersalloyed together.
 6. The engineered material of claim 1, wherein saidmetal microlattice presents a thickness of about 100 μm to 5 cm.
 7. Abearing, comprising: an engineered material including a microlatticeformed of metal, said metal microlattice including a plurality of strutsinterconnected to one another and forming a three-dimensional structure;each of said struts of said metal microlattice including a wallsurrounding an opening; said struts of said metal microlatticepresenting a plurality of interstices; said interstices being present inan amount of 75 to 95 volume percent (%), based on the total volume ofsaid metal microlattice; said engineered material further including alow friction material disposed in said interstices of said metalmicrolattice, said low friction material having a coefficient offriction less than the coefficient of friction of said metalmicrolattice, and wherein said metal microlattice is present in anamount of approximately 15 volume % and said interstices are present inan amount of approximately 85 volume %, based on the total volume ofsaid metal microlattice and said interstices; said metal microlattice isformed of nickel; each of said struts is disposed at an angle of 50° to90° relative to horizontal, has a diameter of about 50 micrometers, anda wall thickness of about 15 micrometers surrounding said opening; saidlow friction material fills said interstices; said low friction materialincludes at least one of polytetrafluoroethylene (PTFE), polyamide(PAI), polyetheretherketone (PEEK), polyethylene (PE), polyoxymethylene(POM), tin, and bismuth; and said low friction material includesparticles selected from the group consisting of ceramic, graphitemolybdenum disulfide, copper, and silver.
 8. The bearing of claim 7including a backing attached to said engineered material, and whereinsaid engineered material presents a sliding surface without a coating ofpolymer material applied to said engineered material.
 9. The bearing ofclaim 7, wherein one area of said metal microlattice includes a greateramount of said metal relative to other areas of said metal microlattice.10. The bearing of claim 7, wherein said metal microlattice presents athickness of about 100 μm to 5 cm.